1. Field of the Invention
The present invention relates generally to knock determination devices and ignition control systems including the same and particularly to such devices and systems that determine from a waveform of vibration of an internal combustion engine whether the engine knocks.
2. Description of the Background Art
Conventionally a technique employed to detect whether an internal combustion engine knocks is known. Japanese Patent Laying-Open No. 2000-205096 discloses an internal combustion engine knock detection device provided for an internal combustion engine and capable of detecting knocking with high precision. The knock detection device disclosed in this document includes a knock detector detecting the internal combustion engine's mechanical vibration to output a knock signal, and a knock determiner determining whether the engine knocks from the knock detector's knock signal in accordance with a reference knock level obtained by a background level BG (i.e., the knock detector's output level provided when the engine does not knock minus a mechanical vibration noise component and an electrical noise component that is multiplied by an adaptation constant K. The knock determiner determines that the engine knocks if a vibration component calculated by subtracting mechanical vibration and electrical components from a peak value of a signal output from the knock detector is larger than the reference knock level, and if the vibration component is equal to or smaller than the reference knock level the knock determiner determines that the engine does not knock.
The knock detection device described in this document can compare a vibration component corresponding to a peak value of a signal output from the knock determiner minus mechanical vibration and electrical noise components with a reference knock level obtained by removing mechanical vibration and electrical noise components to detect with high precision whether an internal combustion engine knocks or not.
The knock detection device described in the above document is, however, disadvantageous in that if the knock detector outputs a signal having a peak large in value the device detects that the engine knocks, and when the engine does not knock and the knock detector nonetheless outputs a signal having a peak increased in value a decision that the engine knocks may erroneously be made.